Roadway markers are mounted on the surface of a roadway, along centerlines, edge lines, to delineate lanes for vehicular traffic.
Examples of commonly used retro-reflective pavement markers using a shell like housing filled with structural polymeric filler material are based on Heenan U.S. Pat. No. 3,332,327, Balint U.S. Pat. No. 3,409,344, or Hedgewick U.S. Pat. No. 5,002,424.
This type of markers is produced in a process consisting of three to four steps:
Firstly, injection molding of a thermoplastic housing (shell), integrally molded with one or two reflective faces, the shell coated with a reflective metallic sealer by a process known as vacuum metalizing, the shell is then filled with a resinous filler material encapsulating the metalized cube corner reflective elements, thereby provide the marker the impact resistance structural body. This type of markers worked well for several months; however, due to abrupt intersection points within the exterior geometric configuration of these markers and the incompatibility of the material composition for forming this type of resinous filled shell markers, often causes pealing and chipping of the reflective face, thereby losing retro-reflectivity. Several method of applying abrasion resistant coating has been used to improve such pavement markers.
Other major development in the pavement marker art has been made; this was achieved by eliminating the use of the metalized sealer for the cube corner reflective elements.
This applicant U.S. Pat. No. 4,726,706, which is incorporated herein by reference in its entirety, divide the inside surfaces of the reflective faces into reflective cells, each cell having multiple cube corner reflective elements, the cells isolated from each other by partition and load carrying walls. Instead of metelizing the inside surfaces, the entire inside surfaces of the reflective faces are sealed with a thin polymeric sheet prior to filling the shell with resinous polymeric filler. The use of resinous filler material for patent '706 made it inherit similar disadvantages as '327 patent.
Other prior art pavement markers have been designed attempting to reduce oncoming tire impact, attain better daytime visibility as well as doing away with the use of resinous filler material.
U.S. Pat. No. 5,667,335 to Khieu discloses a pavement marker comprises of three distinct parts, a base part with structural walls defining hollow cavities, a fiber reinforced shell having two inclined faces with at least one face having raised energy directors within a recessed area and at least one reflective lens plate having cube corner reflective elements; that is, three parts welded together to form the reflective pavement marker of patent '335.
The assignee of '335 patent developed U.S. Pat. No. 6,126,360 to May who essentially used exactly the same exterior geometry and three piece element composition of the pavement marker of '335 patent and attempted to reduce the cost of the same pavement marker, by replacing the fiber reinforced material for forming the (shell like housing) with the same polymeric material which the lens plate and the base part are made of.
U.S. Pat. No. 6,102,612 to Pricone discloses a sun country pavement marker 105 which essentially the same three piece pavement marker of '335 patent with slight change. Marker 105 comprises a body member 110, a top member 130, and one or two reflective lens plates 192 agglutinated within designated recesses. In order to form hollowed body member 110, the top surface is open defining the hollowed body, which is sonically sealed with the additional third member 130 to complete a unitary structural body.
Several prior arts attempted to utilize a unitary structural body for reflective pavement marker fabrication. For example, U.S. Pat. No. 5,392,728 to Spear et al discloses an extruded one piece body with constant cross section having abrupt vertical sides which can be strongly felt during tire impact.
U.S. Pat. No. 4,875,798 to May et al discloses a pavement marker having one piece rigid body supported with partitions walls forming multiple hollow cavities which are open at the base surface. These open cavities at the base eliminated considerable bonding base surface parameter, thereby reduced the bond to the roadway surface.
U.S. Pat. No. 6,109,821 to Montalbano discloses a pavement marker with one piece solid body made of a closed cell foam thermoplastic. This type of material has limited durability due to the air entrapment for creating a low density solid plastic body.
The use of monolithically formed one piece hollowed structural body integrally containing multiple load carrying walls with wedge shaped top ends was disclosed by this Applicant's U.S. Pat. No. 6,267,530 and U.S. Pat. No. 6,579,036. Although the wedged shape top surfaces of the load carrying walls within the recessed area of the front and back faces of the structural body of '036 was deemed to be sufficient for directly welding the reflective lens plate.
However, there was no recognition apparent from the '530 or '036 patents that the cube corner reflective elements need to be within a defined cell like areas within the lens plate defined by partition walls. These partition walls within the lens plate are precisely located to correspond with the locations of the wedged shape energy directors at the top open ends of the load carrying partition walls and the periphery for the recessed faces of the structural body. It has been discovered that by adding a wedged shape top to the periphery walls within the recessed face area of the structural body would enhance bonding the lens plate to the recessed faces of the structural body. This is especially effective when using the standard cube corner reflective lens plate means such as those used in U.S. Pat. No. 3,332,327 to Heenan. However, when micro cube corner reflective means, similar to those used for U.S. Pat. No. 4,875,798, are used to form the reflective lens plates there would be no need to provide wedged shape top to the periphery area within the recessed faces.
Also it has been found that tire impact can be reduced on the reflective faces of present pavement marker through the use of tilted, multi angular sides with protruded intersection regions, which are lower than the pavement marker top periphery.
The present invention pavement marker with tilted, multi angular sides attain better daytime visibility by exposing a larger area of non-reflective surfaces to the oncoming vehicular traffic. A second means of reducing tire impact on the lens plates within the inclined front and back faces of the pavement marker is through the use of multiple circular or rectangular recesses that are open within the base area. The rectangular recesses act as shock absorber when vehicular tire impact the tilted angular sides, thereby minimize damages caused from direct impact on the lens plates.
The goal of this invention is to have a durable pavement marker with high reflectance, low cost and utilizing the monolithically formed one piece structural body having low impact region and internally formed recesses for shock absorption.